I've used **broken link removed** in the past (for a different purpose), it really is a remarkable product, and quite low cost. Basically if it is squeezed, it becomes highly conductive (some quantum tunneling effect apparently).
I used it for a tiny switch (i.e. between two metal plates). It is so neat you don't need any interfacing circuitry for that use-case; it can directly go to a pulled-up microcontroller input because the resistance change is so high from unpressed to pressed.
So, depending on your mechanical arrangement, it may or may not be suitable. I can imagine if you had two long metal strips
and lots of these sandwiched in between then one or more of them would be compressed depending on where the strip was flexed. However, they used to sell it in a very thin, flat sheet form too, which may have been more suitable for your purpose.
The sheet form is very thin (about the thickness of a thin sheet of paper), and is basically about 7cm x 25cm long at a guess.
I have one so I can show a photo of it tomorrow if you like.
The sheet form is actually a plastic sheet with a metal conductive layer, and the quantum material on top. The last few cm of the edge of the sheet exposes the bare conductive layer, but the layer actually is across the whole sheet, and the quantum material is sprayed on top. So, if you have one wire connected to the edge, then pressing anywhere on the sheet with another wire causes the resistance to drop from maybe Mohm down to less than 1kohm. It would need some brainstorming to make a flex sensor, but I imagine it is possible. Maybe the manufacturer still supplies the sheet form.